lkml.org 
[lkml]   [2023]   [Jun]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [BUG] ALSA: core: pcm_memory: a possible data race in do_alloc_pages()
On 26. 06. 23 15:15, Takashi Iwai wrote:
> On Mon, 26 Jun 2023 13:13:21 +0200,
> Takashi Iwai wrote:
>>
>> On Mon, 26 Jun 2023 13:09:00 +0200,
>> Jaroslav Kysela wrote:
>>>
>>> On 26. 06. 23 13:02, Takashi Iwai wrote:
>>>> On Mon, 26 Jun 2023 09:56:47 +0200,
>>>> Jaroslav Kysela wrote:
>>>>>
>>>>> On 26. 06. 23 9:33, Takashi Iwai wrote:
>>>>>> On Mon, 26 Jun 2023 09:31:18 +0200,
>>>>>> Tuo Li wrote:
>>>>>>>
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> Thank you for your reply!
>>>>>>
>>>>>> FWIW, the simplest fix would be something like below, just extending
>>>>>> the mutex coverage. But it'll serialize the all calls, so it might
>>>>>> influence on the performance, while it's the safest way.
>>>>>
>>>>> It may be better to update total_pcm_alloc_bytes before
>>>>> snd_dma_alloc_dir_pages() call and decrease this value when allocation
>>>>> fails to allow parallel allocations. Then the mutex can be held only
>>>>> for the total_pcm_alloc_bytes variable update.
>>>>
>>>> Yes, it'd work. But a tricky part is that the actual allocation size
>>>> can be bigger, and we need to correct the total_pcm_alloc_bytes after
>>>> the allocation result. So the end result would be a patch like below,
>>>> which is a bit more complex than the previous simpler approach. But
>>>> it might be OK.
>>>
>>> The patch looks good, but it may be better to move the "post" variable
>>> updates to an inline function (mutex lock - update - mutex unlock) for
>>> a better readability.
>>
>> Sounds like a good idea. Let me cook later.
>
> ... and here it is.
>
> If that looks OK, I'll submit a proper fix patch.
>
>
> thanks,
>
> Takashi
>
> --- a/sound/core/pcm_memory.c
> +++ b/sound/core/pcm_memory.c
> @@ -31,15 +31,41 @@ static unsigned long max_alloc_per_card = 32UL * 1024UL * 1024UL;
> module_param(max_alloc_per_card, ulong, 0644);
> MODULE_PARM_DESC(max_alloc_per_card, "Max total allocation bytes per card.");
>
> +static void __update_allocated_size(struct snd_card *card, ssize_t bytes)

Missing inline ? May be also used for

> +static void update_allocated_size(struct snd_card *card, ssize_t bytes)
> +static void decrease_allocated_size(struct snd_card *card, size_t bytes)

The rest is fine in my eyes.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>

Thanks,
Jaroslav

--
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

\
 
 \ /
  Last update: 2023-06-26 15:33    [W:0.030 / U:0.216 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site